After upgrading my graphics card to a Radeon RX 7900 XTX the mouse is invisible under X11 session on the KDE version of Manjaro. This bug is also present using a bootable USB of the same version. So, it is independent of my current install. The bug is also present on a clean install of the OS (which is not easy to do with an invisible mouse). The only solution I have found is:
sudo pacman -R xf86-video-amdgpu
After removing that driver the mouse does work and is visible again.